The overall goals of the proposed research are: (1) to understand enough about the thermodynamics of nucleic acid interactions to be able to predict the conformation of a ribonucleic acid molecule on the basis of its nucleotide sequence, and (2) to determine the contribution of different structural elements in a RNA molecule which enable it to bind specifically to protein molecules involved in its function. The basic approach to these goals is synthetic. We have developed powerful methods for the enzymatic synthesis of oligoribonucleotides of defined sequence. Oligomers will be prepared for a variety of physical chemical and biochemical studies. In one type of experiment, advantage is taken of the ability of available single stranded portions of RNA to bind complementary oligomers. By measuring the association constant between an oligomer and RNA, each portion of the RNA molecule may be "assayed" for conformational change or for involvement in a protein-RNA complex. Oligomers binding to RNA can also be used to specifically interfere with the function of the RNA as well. In another type of experiment, oligomers will be made which duplicate portions of the sequence of natural RNA molecules. The secondary structure and the thermal unfolding of these model oligomers will be studied by a variety of spectroscopic methods. The data can be used to predict the conformation of other RNA molecules. The same synthetic fragments can be used to compete for or replace the natural RNA in a specific function. Finally, the development of the T4 RNA ligase reaction will allow enzymatic modification of the nucleotide sequence of a RNA molecule at specifically chosen portions in the sequence. Thus, highly sophisticated structure-function studies on intact RNA molecules can be carried out.